Bioconversion of yolk cholesterol by extracellular cholesterol oxidase from Brevibacterium sp

Expression optimization of recombinant cholesterol oxidase in Escherichia coli and its purification and characterization

Cholesterol oxidase is a bacterial flavoenzyme which catalyzes oxidation and isomerization of cholesterol. This enzyme has a great commercial value because of its wide applications in cholesterol analysis of clinical samples, synthesis of steroid-derived drugs, food industries, and potentially insecticidal activity. Accordingly, development of an efficient protocol for overexpression of cholesterol oxidase can be very valuable and beneficial. In this study, expression optimization of cholesterol oxidase from Streptomyces sp. SA-COO was investigated in Escherichia coli host strains. Various parameters that may influence the yield of a recombinant enzyme were evaluated individually. The optimal host strain, culture media, induction time, Isopropyl ß-d-1-thiogalactopyranoside concentration, as well as post-induction incubation time and temperature were determined in a shaking flask mode. Applying the optimized protocol, the production of recombinant cholesterol oxidase was significantly enhanced from 3.2 to 158 U/L. Under the optimized condition, the enzyme was produced on a large-scale, and highly expressed cholesterol oxidase was purified from cell lysate by column nickel affinity chromatography. K_m and V_max values of the purified enzyme for cholesterol were estimated using Lineweaver–Burk plot. Further, the optimum pH and optimum temperature for the enzyme activity were also determined. We report a straightforward and easy protocol for cholesterol oxidase production which can be performed in any laboratory.

Egg and egg-derived foods: effects on human health and use as functional foods

Eggs are sources of protein, fats and micronutrients that play an important role in basic nutrition. However, eggs are traditionally associated with adverse factors in human health, mainly due to their cholesterol content. Nowadays, however, it is known that the response of cholesterol in human serum levels to dietary cholesterol consumption depends on several factors, such as ethnicity, genetic makeup, hormonal factors and the nutritional status of the consumer. Additionally, in recent decades, there has been an increasing demand for functional foods, which is expected to continue to increase in the future, owing to their capacity to decrease the risks of some diseases and socio-demographic factors such as the increase in life expectancy. This work offers a brief overview of the advantages and disadvantages of egg consumption and the potential market of functional eggs, and it explores the possibilities of the development of functional eggs by technological methods.

Cholesterol to cholestenone oxidation by ChoG, the main extracellular cholesterol oxidase of Rhodococcus ruber strain Chol-4

The choG ORF of Rhodococcus ruber strain Chol-4 (referred from now as Chol-4) encodes a putative extracellular cholesterol oxidase. In the Chol-4 genome this ORF is located in a gene cluster that includes kstD3 and hsd4B, showing the same genomic context as that found in other Rhodococcus species. The putative ChoG protein is grouped into the class II of cholesterol oxidases, close to the Rhodococcus sp. CECT3014 ChoG homolog. The Chol-4 choG was cloned and expressed in a CECT3014 ΔchoG host strain in order to assess its ability to convert cholesterol into cholestenone. The RT-PCR analysis showed that choG gene was constitutively expressed in all the conditions assayed, but a higher induction could be inferred when cells were growing in the presence of cholesterol. A Chol-4 ΔchoG mutant strain was still able to grow in minimal medium supplemented with cholesterol, although at a slower rate. A comparative study of the removal of both cholesterol and cholestenone from the culture medium of either the wild type Chol-4 or its choG deletion mutant revealed a major role of ChoG in the extracellular production of cholestenone from cholesterol and, therefore, this enzyme may be related with the maintenance of a convenient supply of cholestenone for the succeeding steps of the catabolic pathway.

Cholesterol assimilation and biotransformation by Lactobacillus helveticus

Lactobacillus helveticus, grown at 37°C in MRS medium supplemented with 3 mM cholesterol, assimilated all the cholesterol in 42 h having 68 U mg(-1) of intracellular cholesterol oxidase activity. The strain transformed 1 g cholesterol to 0.05 g of androsta-1, 4-diene-3, 17-dione and 0.04 g of androst-4-ene-3, 17 dione within 48 h at 37°C with extracellular cholesterol oxidase activity at 12 U mg(-1) and intracellular oxidase at 0.5 U mg(-1).